Process for the separation of nitrosyl chloride and chlorine



11133 l, 194]- H. ABEEKHUIS, JR 2,247,470

PROCESS FOR THE SEPARATION OF NITROSYL' CHLORIDE AND CHLORINE Filed Aug. 9, 1958 ATTORNEY Patented July 1, 1941 PROCESS FOR THE SEPARATION F NITRO- SYL CHLORIDE AND CHLORINE Herman A. Beekhuis, Jr., Petersburg, Va., assignor to The Solvay Process Company, New York, N. Y., a corporation of New York Application August 9, 1938, Serial No. 223,809

4 Claims.

This invention relates to a process for the treatment of a liquid mixture of nitrosyl chloride and chlorine to recover therefrom a commercially pure chlorine product separate from the nitrosyl chloride. s

It is known that a gas mixture principally consisting of nitrosyl chloride and chlorine such as is obtained by the reaction of .metal chloride and nitric acid may be treated by condensing both the nitrosyl chloride and chlorine to form a mixture of liqueed gases and that the liquid may be distilled to accomplish a separation of a chlorine-rich distillate leaving a nitrosyl chloriderich residue.

I have discovered that a commercially pure chlorine, substantially free from nitrosyl chloride, may be obtained from a liquid mixture of chlorine and nitrosyl chloride by a process of fractional distillation by introducing the liquid mixture into a mid-portion of a rectifying column. In this column the liquid passes downwardly in contact with vapors of nitrosyl chloride to vaporize the chlorine and substantially free the liquid of chlorine, leaving a relatively pure liquid nitrosyl chloride at the bottom of the column. This liquid nitrosyl chloride is boiled and the vapors of nitrosyl chloridethus generated are used, as

n mixture 'entering the column passes upwardly through the upper portion'of the column in contact with a descending stream of liquid chlorine which serves to free the ascending chlorine gas of vapors of nitrosyl chloride. The resulting pure chlorine gas substantially free from nitrosyl chloride isl cooled to condense a portion of it for reiuxing in contact with the vapors in the rectifylng column as described. and the remaining chlorine is withdrawn as a pure chlorine product without reiluxing itin contact with the gases and vapors in the rectifying column.

y I have discovered that in carrying out the process `of this invention as described above; a chlorine product ofl particularly high commercial purity may be obtained when the ratio of liquid chlorine reuxed in contact with the vapors in the distillation column to the chlorine withdrawn as product from the process is:

is the mol ratio of nitrosyl chloride to chlorine in the liquid introduced into the mid-portion of the rectifying column and p is the pressure in atmospheres of the gases in the rectifying column and is no more than about 20 atmospheres. (All pressures given herein are absolute pressures.) When the liquid introduced into the fractionating co1- umn contains about equal proportions of nitrosyl chloride and chlorine, it ispreferred that the ratio of chlorine refluxed in the column to chlorine withdrawn as product be equal to 2 to 3; i. e., that 2 to 3 parts by weight of chlorine be condensed to liquid chlorine and used as refluxdn the distillation column to every one part by weight of chlorine drawn ofi as the pure chlorine product of the process.

I have further discovered that by maintaining a mixture of nitrosyl chloride and chlorine which is being fractionally distilled under a pressure in excess of atmospheric, the eilect of the pressure is to decrease the differential between the partial pressures of chlorine and of nitrosyl chloride in contact with a liquid mixture of the two and thus the dimculues of fraeuonaily eisuumg a',

liquid mixture of nitrosyl chloride and chlorine are increased. I have discovered, however, the adverse elfect upon the fractional distillation oi mixtures of these materials of using pressures of about 4 to 20 atmospheres may be readily compensated for by increasing the effectiveness with which vapors evolved from the liquid mixture are l treated with reiluxed chlorine in the rectiilcation column and that by operating the distllahon and rectiilcation procedure under such pressures in excess of atmospheric, the process as a whole may be made more economic sincethis use or pressure permits of condensing the required liquid chlorine redux at much higher temperatures than when operating at atmospheric pressure and, further. the capacity of a rectiilcation column of a given cross-sectional area is increased. Accordingly, this invention includes a process for the separation of nitrosyl chloride and chlorine from a liquid mixture of the same by distilling the liquid and rectifying the vapors with liquid chlorine condensed therefrom while maintaining the vapors under a pressure of about 4 to 20 atmospheres, preferably under a pressure of 4 atmospheres. By maintaining a pressure of about 8 atmospheres orabove, the chlorine may be condensed by heat exchange with a cooling medium at naturally prevailing temperatures, and under some conditions of plant installation this represents a desirable feature of this invention.

The process of this invention will be more completely described in connection with the following example illustrative of the invention:

The accompanying drawing illustrates an apparatus suitable for carrying out the invention.

In that drawing the numeral I indicates a rectification column of the usual type for the distillation and rectication of a liquid mixture provided with means, not shown in the drawing, such as bubble platesor packing for intimately contacting liquid descending through the column with ascending vapors. The bottom of the column is provided with a heater 2 and a liquid draw-off 3; The top of the column is provided with a gas draw-off 4 leading to a cooler 5 from which a mixture of liquid andgas flows to a separator 6. A pipe 1 for return of liquid from separator 6 to the top of column I and a draw-off for gas 8 from separator 6 are provided.

In employing the apparatus illustrated in the drawing for carrying out the processA oi this invention, a liquid mixture of nitrosyl' chloride and chlorine is introduced through a pipe 9 into a mid-portion of rectifying 1 column QI. Liquid nitrosyl chloride in the bottom of the rectifying column 'is boiled by means of heat ysupplied through heater 2jand the vapors thus obtained passupwardly in the 'column in contact with the descending liquidmixture. The nitrosyl vChlo'- ride is .vaporized in amount suflicient to` sube stantially free the incoming liquid of chlorine while the remaining jliquid nitrosyl chlorideis drawn from the bottom of column I through draw-,01T 3. The `vaporized chlorine ascends through the top of column I and passes through pipe 4 to cooler 5 where a part of the. chlorine isv` liquefied by indirect heat exchange with refrigerated brine. In separator 6 the liquei'ledchlo-v rine is separated from the remaining-gaseous chlorinevand the liquid isreturned through pipe. 1 to the top of column I to provide reflux for the treatment in the top of Athe column of the vapors The chlorine gas separated from 4the liquid chlorine in sepa rator 6 is drawn ofi as product through 8. The; liquid nitrosyl chloride in the mixture intro-y duced into the rectifying column flows to the; bottom of. the column and is boiled to provide the vapors'for treating the incoming liquid toascending through the column.

free it of chlorine.

The mixture of uquid nitrosyl moi-ide and chlorine to ybe. treated in accordance with the process'of'this example may contain about equal proportions of the two constituents and bey pumped into rectication column I while maintainingfthe. column under a pressure of 4 atmospheres by means of valves I `and Il in drawintroduced into the column. However, the liquid may be introduced at a point somewhat above or below this point, although this will entail some sacrifice in efficiency of the column. In cooler 5 the chlorine vapors leaving the top of the column are cooled suciently to condense two-thirds to three-fourths of th`e chlorine which is returned as chlorine reflux to the top of column I while the remaining uncondensed onethird to one-fourth of the chlorine is withdrawn through draw-.off 8 as a commercially pure chlorine product. With the vapors in the rectifying column being maintained under a pressure of about 4 atmospheres, the desired liquid chlorine reflux may be condensed in lcooler 5 by cooling the chlorine to about 0 C.

The foregoing example may be modified in many respects without departing from the invention. For example, the desired liquid chlorine reux for rectifying column I may be obtained by providing cooling coils in the top of the column itself and supplying to these cooling coilsa cooling medium at a temperature suitable for condensing the desired amount of reflux liquid chlorine which is permitted to flow downwardly in the column while `the uncondensed chlorine gas is withdrawn from the top of the column as product. Instead of condensing in cooler 5 only a portion of the chlorine gas leaving the top of column I, all of the gaseous vchlorine leaving'column I may be condensed in cooler 5 and a portion of the condensed liquid chlorine returned to the top of column I while another portion is column, the liquid nitrosyl chloride flowing to thebottom of the column may be passed into a separate vaporizer where it is'boiled to provide the vapors of nitrosyl chloride for treating the liquid mixture in the bottom ofthe rectifying,

column. The puried nitrosyl chloride product of the process may be withdrawn from thisI vaporizer eitheras liquid or as gas.

The process described herein may be modiLied to introduce into the mid-portion of the rectil-A cation column a gaseous mixture of nitrosyl` ois B'and 3. 'Thepreferred mid-point oi column I-into ywhich the liquid mixture is introduced is that point at which the composition-of liquid iri the column withrespect to nitrosyl chloride and chlorine contentl is the same as the liquid.y

chloride and chlorine. Inthusfoperating, the mixture will be treated in thecolumn by means of the vapors of nitrosyl chloride passing up-v wardly and the reflux of liquid chlorine passingdownwardly therein. Except that when the mix-Y ture is' introduced into the rectification column;

as a gas,v it will preferably be introduced at a mid-point of the column Where the vapors or:

gases in the column have the same composition as the entering gases, the process taking place in the column and the conditions of operation mersed in a cooling medium. Accordingly, when the mixture of nitrosyl chloride and chlorine is introduced into the rectifying column as a mixture of gases, the ratio of 4chlorine refluxed to that withdrawn as product is maintained in the range of is the mol ratio of nitrosyl chloride to chlorine in the condensate which would initially form upon cooling the gas mixture to a temperature at which the gas is partially liqueed.

This application is a continuation-impart of my co-pending application Serial No. 696,138, led November 1, 1933, now United States Patent No. 2,130,519, granted September 20, 1938.

I claim: l

1. The process for the separation of a mixture of liquid nitrosyl chloride and chlorine which comprises continuously introducing said liquid mixture into a mid-portion of a rectifying column, passing the liquid mixture downwardly in the column in contact with vapors of nitrosyl chloride to vaporize the chlorine and substantially to free the mixture of chlorine leaving relatively pure nitrosyl chloride, continuously boiling the liquid nitrosyl chloridethus free from chlorine to vaporize nitrosyl chloride,passing vapors of nitrosyl chloride thus obtained upwardly in said column in contact with the descending flow of liquid mixture, passing the chlorine gas vaporized from the liquid mixture upwardly through said column in contact with a descending stream of liquid chlorine to free the chlorine gas of vapors of nitrosyl chloride, cooling the thus treated chlorine gas to liquefy it at least inpart, passing thus liquefied chlorine as a liquid chlorine reflux in contact with the gases and vapors ascending through said rectifying column, continuously withdrawing another portion of said' last mentioned chlorine gas as substantially pure chlorine product without refluxing it in said column, the ratio by weight of liquid chlorine refluxed to said chlorine withdrawn as product corresponding to 1(0.6-l-NOCl NOCI is the mol ratio of nitrosyl chloride and chlorine in said liquid mixture introduced into the rectifying column and p is the pressure (in atmospheres) in said column, and continuously withdrawing nitrosyl chloride from the bottom of said column.

2. vThe process for the separation of a mixture of liquid nitrosyl chloride and chlorine which comprises continuously introducing said liquid mixture into a mid-portion of a rectifying column, passing the liquid mixture downwardly in the column in contact with vapors of nitrosyl chloride to vaporize the chlorine and -substantially to free the mixture of chlorine leaving relatively pure nitrosyl chloride, continuously boiling the liquid `nitrosyl chloride thus freed from chlorine to vaporize nitrosyl chloride, passing vapors of nitrosyl chloride thus obtained upwardly inl said column in contact with the descending ilow of liquid mixture, passing the chlorine gas vaporized from the liquid mixture upwardly through said column in Contact with a descending stream of where NOCZ C12 is the mol ratio of nitrosyl chloride and chlorine in said liquid mixture introduced into the rectifying column and p is the pressure in atmospheres in said column, continuously withdrawing nitrosyl chloride from the bottom of said column, and maintaining the gases and vapors in said rectifying column under a pressure of about 4 to about 20 atmospheres.

3. The process for the separation of a mixture of liquid nitrosyl chloride and chlorine which comprises continuously introducing said liquid mixture into a mid-portion of la rectifying column, passing the liquid mixture downwardly in the column in contact with vapors of nitrosyl chloride to vaporize the chlorine and substantially to free the mixture of chlorine leaving relatively pure nitrosyl chloride, continuously boiling the liquid nitrosyl chloride thus freed from chlorine to vaporize nitrosyl chloride, passing vapors of nitrosyl chloride thus obtained upwardly in said column in contact with the descending ilow of liquid mixture, passing the chlorine gas vaporized from the liquid mixture upwardly through said column in Contact with a descending stream of liquid chlorine to free the chlorine gas of vapors of nitrosyl chloride, cooling the thus treated chlorine gas to liquefy it at least in part, passing thus liquefied chlorine as a liquid chlorine reux in contact with the gases and vapors ascending through said rectifying column, continuously withdrawing another portion ci said last mentioned chlorine gas as substantially pure chlorine product without refluxit in said column, the ratio by weight of liquid chlorine refluxed to said chlorine withdrawn as product corresponding to about 2 to about 3 parts of reiluxed chlorine to one part of chlorine withdrawn as product, maintaining the gases and vapors in said rectifying column under a pressure of about 4 atmospheres, and continuously withdrawing nitrosyl chloride from the bottom of said column.

4. The process for the separation of a mixture of nitrosyl chloride and chlorine which comprises continuously introducing said mixture into a midportion of a rectifying column in which the mixture is directly contacted with a reflux of liquid chlorine flowing downwardly in the column and vapors of nitrosyl chloride passing upwardly in the column, passing the liquid flowing downwardly in the column in contact with the upwardly flowing vapors of nitrosyl chloride to vaporize the chlorine and substantially to free the liquid of chlorine leaving relatively pure nitrosyl chloride, continuously boiling the liquid nitrosyl chloride thus free from chlorine to form said vapors of nitrosyl chloride which pass upwardly in said column in contact with the descending ow of liquid, passing the chlorine gas in the column upwardly through said column in contact with' is the mol ratio of nitrosyl chloride and chlorine in said first mentioned mixture when it is introduced into the rectifying column as a mixture of liquid nitrosyl chloride and chlorine and when said first mentioned mixture is introduced into the rectifying column as a mixture of gaseous nitrosyl chloride and chlorine, said N OCZ C12 is the mol ratio of nitrosyl chloride and chlorine in the condensate which would initially form Y upon coolingsaid rst mentioned mixture to a temperature at which the gas is partially liqueed, and p is the pressure in atmospheres) in said column, and continuously withdrawing nitrosyl chloride from the bottom of said column.

VHERMAN A. BEEKHUIS, JR. 

